The present invention relates to an electrostriction effect element utilizing a known longitudinal electrostriction effect, and to an improved structure for particularly facilitating electrical connections between a pair of external electrodes of a multilayer piezoelectric actuator element and a pair of lead wires.
Such an actuator element is regarded as a substantial element in the field of mechatronic equipment as well as sensor elements. The actuator is a kind of transducer whereby electric energy is transduced into mechanical energy such as displacement or force. In U.S. Pat. No. 4,523,121 issued on June 11, 1985, a novel multilayer actuator element is proposed by the present applicant to improve a defect of short repetitional life prevailing on a prior art stacked type actuator, wherein a multiplicity of sintered piezoelectric plates were stacked on one another by using adhesive material.
In a newly proposed multilayer actuator, a plurality of green sheets of piezoelectric material with a conductive paste for an internal electrode formed on one side of the green sheet are laminated and sintered to form an integrated laminated structure. A first group of insulator belts are formed on every other end of the internal electrodes exposed to one of opposing side surfaces of the laminated structure, and a first external electrode layer is formed on exposed ends of the internal electrodes which are not covered by the first group of insulator belts, thus forming a first electrode group. A second group of insulator belts are also formed on the exposed ends of the internal electrodes which are not electrically connected to the first external electrode layer on the other of opposing side surfaces, and a second external electrode is formed thereon, thus forming a second electrode group. Then, a pair of lead wires are connected to the external electrodes on both sides. In such an electrostriction effect element, when a voltage is applied between the external electrodes through the lead wires, the applied voltage is provided on both ends of all the electrostriction sheets through the internal electrodes, and thus electrostriction is generated in the direction of lamination as the whole element.
Connecting portions between the lead wires and the external electrode layers are arbitrary. However, a general connection means such as solder or the like may involve the following problem. When the connecting portions are chosen at the upper end or the lower end of the external electrode layers in the direction of lamination, care should be taken such that since a metallic cap is mounted on both upper and lower portions of the actuator in many cases, solder may be applied erroneously on the metallic cap if a soldering position of the lead wire comes on the upper end or the lower end of the adtuator. As a result, excessive attention must be paid to the soldering process.
It is therefore preferable that the lead wire be soldered at the central portion of the external electrode layer. However, if each electrostriction layer is thinned, for example, to 250 .mu.m or below, then there no longer will be sufficient space for the soldering process. Over soldering of the external electrode layer and rupture of the insulator due to a strain suppression effect of the solder may cause problems in reliability.